Tobacco sheet is a reconstituted tobacco recombinated by using tobacco wastes, such as tobacco dust, stem, scrap and some parts of low-grade tobacco-leaf formed during cigarette manufacture process. First, it can save tobacco materials as many as possible to reduce cigarette cost; second, tobacco sheet play an important role in reducing tar and minimizing the harm of cigarette. There are basically two commonly but quite different commercially employed processes used for the preparation reconstituted tobacco. One procedure, referred to commonly as band casting, employs a slurry of finely divided tobacco parts and a binder which is coated onto a steel band and then dried. The sheet made by such procedure has less filling capacity and it has less contribution to tar release reduction when it blended in cigarette composition. In addition, waste or scrap tobacco parts or dust are normally bound together by providing an adhesive to give the tobacco sheet coherence, the compound of the adhesive pyrolysis will inevitably enter into smoke during cigarette smoking, which will decrease smoke quality of cigarette. The second known process employs papermaking techniques. Its physical performances and filling capacity are much better than that made by slurry process and it can more effectively reduce tar in cigarette smoke and minimize its harm. With increased public attention focused on health and smoke, relative authorities enhance control on tar of cigarette products step by step, which makes papermaking process tobacco sheet have more and more important position in cigarette composition.
In the papermaking process, the soluble ingredients of natural tobacco are extracted. The tobacco may be macerated or comminuted in preparation for extraction. The extraction is normally performed by use of water. The extract is separated, and the insoluble fibers with or without additives are transformed into a self-sustaining web by the usual papermaking technique. The tobacco extract, which may be concentrated to a liquor, is then reapplied into the web. The application of the extracted tobacco material may be achieved in any appropriate manner, as by spraying, saturating, or otherwise.
U.S. Pat. No. 4,182,349 revealed an improvement for production method of papermaking process tobacco sheet, by which stalk is separated from other parts for respective treatment. Its target is to heavily thresh ligneous part of the stem, and then the heavily threshed stalk is mixed with other parts for further threshing. This patent also released that before threshing, the stalk and other parts are respectively extracted by water, and the extracts are mixed and concentrated, which is then coated on the sheet base shaped by slurry. The patent further disclosed that some part of stalk extract could be abnegated.
U.S. Pat. No. 4,962,774 and U.S. Pat. No. 4,131,117 revealed a production method of tobacco sheet. In these patents, tobacco stem and leaf is not treated respectively. These patents focused on the treatment of tobacco extracts. U.S. Pat. No. 4,131,117 disclosed a re-crystallization process to remove kalium salts in extract, but U.S. Pat. No. 4,962,774 suggested treatment of the extract by ammonia.
In process of tobacco sheet production by papermaking methods mentioned above, there are several technical shortcomings:    1. Because the raw materials used in production of papermaking tobacco sheet are tobacco stem and leaf scrap (their diameters are over than 1 mm), the tobacco dust or ash with size of less than 1 mm cannot be used, resulting in waste of tobacco materials.    2. The prepared tobacco sheet has heavier woody note and impurity taste that will decrease smoke quality of the sheet smoke.    3. Traditional technics of producing tobacco sheet by papermaking method is mainly based on traditional papermaking method, in which the papermaking parameters, with target to ensure paper's smooth and compactness, are used as technics parameters of its beating degree in defibrilation technics of stem and leaf scrap. But in tobacco sheet process, requirements on tobacco sheet are looseness and roughness that is directly related with filling capacity of tobacco sheet, more looseness and roughness of the tobacco sheet, the higher filling capacity will be. Therefore, the beating degree of original traditional papermaking method cannot satisfy with requirements to produce quality tobacco sheet.
Terms involved in this invention are explained as follows:
Tobacco stem: Through threshing/redrying stem-lamina separation process, leaf is separated into leaf veins and leaf body, of which the separated leaf veins is called as tobacco stem.
Leaf scrap: Through threshing/redrying stem-lamina separation process, leaf is separated into leaf veins and leaf body, of which the separated leaf body in diameter of 1˜6 mm is called as leaf scrap.
Tobacco dust: In the whole tobacco treatment process, scraps formed in mechanism, transportation and etc. in sizes of 2 mm and smaller, or processed leaf scraps in sizes of 2 mm and smaller, are called as tobacco dust.
Defibrilation: It refers to threshing tobacco stem or leaf and etc. that have been treated by hot water macerating and solid/liquid separation, by using general equipment well known in the professional field.
Sheet quality evaluation: It is divided into physical characters/data evaluation and sensory quality evaluation. Physical characters/data evaluation includes tensile strength, thickness, moisture and combustibility that are tested by professional organization and professional inspection devices to judge if they are qualified or not with reference of industrial standards; sensory quality evaluation is conducted by professionally-trained expert group to evaluate smoke data such as flavor and aroma, full, irritancy, offensive taste, aftertaste, impact and etc.